- Objectives: Serum levels of prolactin, interleukin-1 [IL-1], interleukin-2 [IL-2], and interleukin-6 [IL-6] were determined in patients with the irritable bowel syndrome [IBS], both IBS and the fibromyalgia syndrome [FMS], and matched healthy normal controls [HNC]. The purpose of this pilot study was to evaluate whether serum levels of these cytokines correlate with the presence of either or both of these functional disorders and with their severity. Methods: A study of 76 IBS patients [Rome criteria] with 68 HNC matched by age and gender. Participants completed detailed questionnaires and were tested for FMS. Serum levels of IL-1, IL-2 and IL-6 were determined for all participants using the enzyme-linked immunosorbent assay method, and prolactin levels were determined by the immunoradiometric assay. Results: Although patients with functional disorders [IBS-only or both IBS and FMS] had more severe symptoms and complaints than HNC, there were no significant differences in serum prolactin or cytokine levels between these groups. Conclusions: Serum prolactin and IL-1, IL-2, and IL-6 levels do not differentiate between patients with functional disorders and HNC, and are not correlated with severity of the disorder.